Information handling systems utilize high speed printers for rapidly generating printed information in a tangible form. High speed printers generally utilize xerographic or impact printing technologies. Impact printers are selected where the option to print multipart forms is desired. The printing mechanism for impact printers generally transfers ink or other material from a print ribbon onto the paper to form images on one major surface of the paper.
Continuous-form paper is usually supplied from a box in which the paper is stacked in a fanfold pattern. The paper may be single layer or may be multi-layer to provide multi-part forms. Continuous-form paper is perforated along lateral lines for dividing the continuous length into separable rectangular sheets or forms. Each of the separable sheets is rectangular and is typically 11.5 inches high by 14 and 7/8 inches wide. The paper is folded along the perforations in a zigzag manner reminiscent of oriental hand fans in which each lateral perforation is folded in the opposite direction from the preceding fold to form a stack.
Tractor drives engage a longitudinal row of holes along each edge of the paper for moving the paper longitudinally from the source box of paper, through the printing mechanism and downward toward a horizontal surface upon which it refolds into an output stack of printed, continuous forms. The tractor drives tend to distort the paper at the tractor holes in the edges of the paper so the refold stack is bowed upward at the edges. Typically, the paper length remains slightly folded along the lateral perforations after unstacking and printing and the descending paper length naturally tends to refold onto the stack at each lateral perforation in the same direction at it was originally folded.
In order to aid in establishing the proper initial stack position and fold direction of the refolding stack, some printers such as the IBM 3262 and IBM 6262, provide a set of multiple chains hanging from the printer frame on each respective side of the descending length of paper. The lower ends of all the chains extend down to hang approximately 4 inches above the platform on which the output forms is folded. In at least one case at least one of the chains on at least one of the sides of the paper is extended so that the end of the chain was substantially less than 4 inches above the platform. Once the stack is started in the proper location with the continuous length of paper refolding in the previous fold directions, proper refolding tends to continue without any additional aid. However, occasionally the paper fails to refold in the desired direction which produces an unfolded jumble of printed output, and if not detected in time the paper stops moving through the printer. These previous chain configurations do not prevent occasional output jams from occurring during printing.
Since the introduction of fanfold paper refolding, practitioners have faced the problem that occasionally the paper will fail to refold along the lateral perforations in the proper direction, resulting in an output paper jam. It is known that the jamming is related to the bowing of stack due to the tractor damage and to the height of the paper discharge above the top of the stack and is also related to the intermittent characteristics of feeding of the paper through the printer.
The longitudinal movement of the paper through the printer is not continuous. Usually the movement is stopped as each line is printed on the sheets. Also, the paper tends to move quickly through blank lines and even more quickly through blank pages. For a very high speed paper tractor, the paper output is often accelerated so that descending paper bends as it falls into the stack and fails to properly refold onto the stack.
Also, the printer does not usually operate continuously. The output typically consists of separate reports which are sent to the printer as desired so that the printer is idle for minutes or even for hours between jobs. In addition, information handling systems tend to be idle for long periods due to schedules of working shifts, weekends and holidays. The paper in the printer may be idle with a lateral perforation in a straightened configuration so as to forget the original fold direction at the perforation; or the paper may be idle in a bent configuration and retain the bend so that it does not properly refold onto the output stack.
In order to overcome this occasional jamming, practitioners have implemented many complex paper handling schemes. For example in U.S. Pat. No. 4,504,051 to Bittner et al. the height of a platform on which the printed output is stacked is automatically adjusted so that the distance from the paper output of the printer and the top of the stack remains about one half the height between the successive folds at the lateral perforations. FIG. 5 of that patent shows weighted beads or chain links on each side of the fanfold paper as it exits downward.